The present invention relates to a method and a device for controlling a wiper motor.
Numerous conventional methods of controlling a wiper motor involve adjusting the response sensitivity of a rain sensor as a function of an additional brightness sensor.
A method of adjusting the response sensitivity of a rain sensor is described in German Published Patent Application No. 41 34 432 in which the response sensitivity may be adjusted by an additional brightness sensor or by a switch-on signal of a light switch. In addition, it is conventional that the amplification of a rain sensor signal may be influenced by the external protective circuit as a function of the ambient brightness.
However, in all of these methods and devices, residual wetness is frequently encountered on the windshield, which is troublesome, especially in darkness.
The method according to the present invention may provide the advantage that residual wetness, which may still be present on the windshield after the wiper motor has been switched off, is detected and removed.
After it has stopped raining, streaks often remain on the windshield which do not dry by themselves and which may thus represent residual wetness. By re-evaluating the signals from the rain sensor after a defined time after the wiping operation has ended and checking against a second threshold, one or more additional wiping operations may be triggered, as needed. In this manner, the residual wetness is removed, thereby significantly improving visibility.
An additional significant advantage may be realized when this method is supplemented by an ambient brightness signal, using a brightness sensor, and the wiper motor is actuated at a defined change in the ambient brightness. In this manner, consideration is made for the fact that residual wetness on the windshield is even more troublesome in darkness than in normal daylight.
This significant advantage may be realized when entering tunnels or parking garages in which the ambient brightness quickly changes from light to dark. If the wiper motor was in intermittent operation, for example, before entering, the windshield is normally wet upon entering the tunnel. After entry has been recognized by detection of the change in the ambient brightness, it possible to trigger a wiper operation and thus remove troublesome residual wetness.
In such cases it may be of further advantage when the wiper motor is actuated for only a single wiper cycle. Although residual wetness is generally troublesome, there is little associated moisture. The residual wetness may thus be removed in one wiper cycle, thereby preventing abrasive stress such as rattling or squeaking of the wiper on the windshield.
Furthermore, it may be advantageous when the wiper motor is actuated only when a moisture exceeds or drops below a threshold of the rain sensor, since in this manner it is possible to prevent dry friction of the wiper against the windshield.
The device according to the present invention may provide the advantage that visibility-impairing residual wetness remaining on the windshield caused by unevaporated smears or drops may be removed.
It may be advantageous when the trigger stage includes a first threshold value analyzer which compares the signals to a first threshold and which is connected, via a delay element connected to a timer, to a second threshold value analyzer which compares the signals to a second threshold and which triggers a single wiper cycle when the second threshold is exceeded or is not reached. A simple and practical device for removing residual wetness on a windshield is thus provided.
If this device also includes a brightness sensor, the trigger stage actuating the wiper motor at a defined change in brightness when the wiper motor has already been actuated within a predetermined time, the history of the wiping operation may thus be advantageously taken into account. If a continuous wiping operation was still in progress two minutes, for example, before a large change in brightness, it may be concluded with reasonable certainty that residual wetness is still present on the windshield.
In addition, it may be advantageous when the device has a brightness analysis stage which compares the changes in signals from the brightness sensor to the defined change in brightness.
If the timer or the delay element also includes a flag indicating a wiper cycle which is reset only after a predetermined time has elapsed, it may be determined at any time whether a wiper cycle has been triggered or ended within a predetermined historical time period.
It may be of significant advantage if the evaluation stage is configured in such a manner that it triggers a single wiper cycle only when the flag of the timer or delay element is simultaneously set and the threshold of the defined change in brightness is exceeded or is not reached. Thus, a single wiper cycle is triggered only when the brightness analysis stage gives a positive result and the last wiping operation has occurred fairly recently, since in this case it may be concluded that residual wetness is present on the windshield.
Example embodiments of the present invention are illustrated in the drawings and described in the following description.